1. Field of the Invention
The invention is directed to a method for determining the dynamic Poisson's ratio of a material through nondestructive testing.
2. Description of Related Art
When planning out the material of different types of construction buildings, mechanical equipment, tools, electrical products, mold assemblies, electric equipment, and others, deformation results when sustaining temperature, weight, static, and dynamic loads from external forces, and so the Poisson's ratio of the equipment composition material must first be determined. Generally, there are two methods to measure the Poisson's ratio of a material: static Poisson's ratio measurement method and dynamic Poisson's ratio measurement method. The dynamic Poisson's ratio measurement method is a nondestructive test. Because the tested specimen will not be damaged, and the testing process is relatively quick, the dynamic Poisson's ratio measurement method is widely received by industry and education by applying to practical applications and educational research.
The CNS (Chinese National Standards) standard does not have related determining methods for measuring the dynamic Poisson's ratio of a material. In the United States, in the ASTM E1876 (Standard Test Method for Dynamic Young's Modulus, Shear Modulus, and Poisson's ratio by Impulse Excitation of Vibration) standard, even though there is an explanation for a determining method for measuring the dynamic Poisson's ratio of a material, when the determining method is put in practice, the dynamic elasticity modulus and dynamic shear modulus of a solid long rod material specimen must first be determined, then by repeated calculations through an iteration method, the dynamic Poisson's ratio of the material is obtained. Besides the determination method being complicated, the ASTM E1876 belongs to a technique of free resonance by impulse excitation type method, and the standard especially explains that this method is difficult to precisely obtain the dynamic shear modulus of a circular rod, thus causing the standard obtained dynamic Poisson's ratio of a material to have uncertain factors.
Furthermore, when using the determining method of ASTM E1876 to determine the dynamic Poisson's ratio of a circular solid rod specimen, the fundamental longitudinal resonant frequency or the fundamental flexural resonant frequency of a circular solid rod specimen must first be measured, to determine the dynamic elasticity modulus. Then the fundamental torsional resonant frequency is measured, to determine the dynamic shear modulus. After measuring the dynamic elasticity modulus and the dynamic shear modulus, the dynamic Poisson's ratio of the circular solid rod is calculated. In the standard, the testing specimen length/diameter ratio is required to be greater than 20, thus the difficulty in the fabrication of a circular rod specimen is increased. Otherwise, iterated calculation in the method is required until the deviation is less than 2%, and a more precise dynamic Poisson's ratio of a material is obtained.
Nevertheless, when determining the circular solid rod specimen dynamic shear modulus, the required torsional resonant frequency is difficult to obtain through testing. In the ASTM E1876 standard, the determination method of the torsional resonant frequency of a specimen is not clearly explained through drawings. Thus, the invention further explains through, for example, the ASTM C215 (Standard Test Method for Fundamental Transverse, Longitudinal, and Torsional Resonant Frequencies of Concrete Specimens) standard to measure the dynamic shear modulus of a solid rod specimen. As shown in FIG. 1A and FIG. 1B, the measuring method sticks an accelerometer receiver 110 onto an L shaped metal material 120 using hot glue. Then, the L shaped metal material 120 is fixed on a rod specimen 130 surface, and tangent line directions of the section of the accelerometer receiver 110 and the rod specimen 130 section maintain parallel. When undergoing impact, the impact force needs to be acted along the tangent direction of the surface of the rod specimen 130. Thus, processes of the determining method are complicated and difficult, and the torsional resonant frequency is hard to obtain.